LONDON — Matthew Barzun, the American ambassador to the Court of St. James’s, stood before a buzzing, boisterous audience of several hundred teenagers in a poor borough on the southern edge of greater London and asked them what frustrated or concerned them the most about the United States.

The responses came quickly: racism, police brutality, guns, the justice system, Middle East policies, American meddling in the world.

These students at Oasis Academy Shirley Park, in Croydon, were unusual, Mr. Barzun told them. This is the 104th school he has visited in Britain, talking to some 10,000 sixth-formers (high-school seniors), “and at almost every school I’ve been to,” he said, “guns comes up first.”

It is an unusual exercise in outreach and public diplomacy pressed by Mr. Barzun, 45, an entrepreneur, top fund-raiser for President Obama and former ambassador to Sweden. Mr. Barzun sees the risk of drift in what Winston Churchill called the special relationship between the United States and Britain. That risk is especially acute in a generation with members who were 4 years old during the Sept. 11 attacks and who have a different set of memories and concerns, like the wars in Iraq and Afghanistan.

The rise of the Islamic State was by far the most important policy issue to the students, who voted with electronic clickers, trailed by climate change, peace in the Middle East and Britain’s European Union membership.

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Students who included guns as one of their main concerns about the United States showed their lists during Mr. Barzun's visit.CreditAndrew Testa for The New York Times

Oddly, perhaps, given the news coverage here, Edward J. Snowden and surveillance abuses did not come up at all.

“My hunch was that young people wouldn’t have as strong an affinity to the special relationship as older generations,” Mr. Barzun said afterward. Talking to sixth-formers, who are 16 to 18 years old, rather than university students studying international relations, was a way to “get a different set of issues,” he said, “and it wouldn’t all be just classic foreign policy,” but domestic concerns, too, like American racial attitudes and guns.

This state-funded school of 1,600 students, which is sponsored by a Christian charity, Oasis, is more ethnically diverse than the average in Britain. According to Chris Webbe, head of the sixth form, some 26 percent of the students are white British, compared with the national average of 70 percent; 13 percent are of black African heritage, compared with 3 percent; 14 percent are of black Caribbean heritage, compared with 1 percent; and 69 percent have English as their first language, compared with 82 percent nationally. The students here speak 42 languages.

But their responses were similar to those of students all over Britain, in state schools as well as private ones like Eton, Mr. Barzun said.

Working with a colleague writing answers on a whiteboard, Mr. Barzun asked the students to think about good and bad outcomes when the United States gets involved in the world. On the good side, students mentioned the two World Wars, and Mr. Barzun the Marshall Plan. On the bad, there was chaos in Iraq; Mr. Barzun raised Vietnam.

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The rise of the Islamic State was an important policy issue to these students, along with climate change, peace in the Middle East and Britain’s membership in the European Union.CreditAndrew Testa for The New York Times

Then, he asked, what happens when Washington stays out? On the bad side, a student suggested Syria and the rise of the Islamic State. Rwanda, Mr. Barzun said, reminding them that up to half a million people died there.

“What are examples when the U.S. stays out and good things happen?” he then asked. “Soccer,” a student said, bringing laughter, and Mr. Barzun said quickly, “We’re going to win the World Cup one day,” causing more amusement.

But his point, he said, which was “too simple,” was also clear. “Good things don’t happen when the U.S. stays out — bad things happen.” Then he raised the Nazi bombing of London while the United States stood by, entering even World War II rather late. “So how do you get the United States involved, but where it helps?” he asked, saying that this issue was at the heart of the Obama presidency.

When he first went abroad, he told the students, he asked Mr. Obama what advice he would give a new diplomat. Mr. Obama responded, “ ‘Matthew, listen —’ ” Mr. Barzun said, “and I slowly realized that’s what he meant, to listen.”

Then Mr. Barzun told the students, “You are the future leaders of the U.K., and I want to learn what’s on your mind.”

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After visiting 100 schools, the American Embassy in London put together a word cloud illustraing what students said frustrated them, or they most disliked, about the United States.CreditUnited States Embassy in London

Later, he said, “I want to give them room to be able to disagree,” not to force arguments on them. “If you go in thinking you’re in the argument-winning business, you can end up seeing a lot of arms folded,” he said. “But if you listen, people hear you differently.”

The reviews were good. Euphrose Tambwe, 16, said, “He asked us what we thought and then explained what he thought.”

She stopped for a moment. “It was really his honesty that got me,” she said. “I thought he’d come to say ‘America is great and don’t believe the media,’ and the fact that he admitted mistakes struck me.”

Meggie Eloy, 16, said she was impressed that the American ambassador was visiting schools. “He’s planting the seed and leaving it to us,” she said.

James Clayton, 18, remembered that Mr. Obama had called France “our oldest ally,” and “that showed we need to rebuild the relationship,” he said. “It’s possible to work together.”

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The most common responses when students were asked what they most liked, admired or found inspiring about the United States.CreditUnited States Embassy in London

Ms. Tambwe said Mr. Barzun had not changed her views much, “but it made me think a bit more about America and what it stands for.”

Louise Lee, 33, has been the principal of the school since January. “He’d make a good teacher,” she said, laughing.

“I knew it was about taking a message to students, but that it would be interactive, and controversial topics would not be off-topic,” she said. “It was much more low-key than I expected, and more accessible.”

Mr. Barzun also asked students what they liked about America, or what inspired them. One student said, “The boss” — referring not to Bruce Springsteen, whom another student named, but to Mr. Obama. Others said culture, Hollywood, Stan Lee of Marvel Comics, opportunity, video games and Michael Jackson. One even said the C.I.A.

Then another student said, “We’re different, but we’re not super different,” and Mr. Barzun leapt at that, saying he would use it in future talks.

“These are not tuned-out kids,” Mr. Barzun said later. “They’re not apathetic, and the fact that they hold us to high standards I think is really good, because they ought to, and because we ought to rise to it.”

Next year is the 70th anniversary of the much-mocked special relationship, a phrase coined by Mr. Churchill in a famous speech in Fulton, Mo., in March 1946. The relationship took a big hit from the wars in Iraq and Afghanistan and the sense that Britain has been too subservient to American demands. But Mr. Barzun is a relentlessly cheerful man.

“What we’re trying to do at the embassy is focus forward on what the next 70 years is going to look like,” he said. “That group of kids and others like them are the new foundation that’s going to be built upon, and I don’t want to neglect that.”

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A version of this article appears in print on , on Page A6 of the New York edition with the headline: An Ambassador Builds Diplomatic Bridges With Teenagers. Order Reprints | Today’s Paper | Subscribe